In recent years, the interest in performance of buildings (structures) in terms of earthquake resistance has increased. Thus, the soundness of a building at the time of an earthquake may be monitored by providing measurement means that measures information related to the deformation of a structure such as an accelerometer, a strain gauge, or a displacement gauge.
Then, data measured by these measurement means is sent to a data monitoring room or the like away from a site and the data is collected through a data analysis computer or the like. The data analysis computer calculates inter-story deformation of the building and compares the calculated inter-story deformation with a setting value to determine whether there is damage to the building, and a determination result is used, for example, to evaluate soundness and check safety after an earthquake occurs (for example, see Patent Document 1).
In addition, a method for determining damage to a building caused by an external force such as an earthquake or a strong wind or aging deterioration of structural materials based on measurement of a microtremor is also used (for example, see Patent Document 2). Here, in Patent Document 2, a damaged portion of a building is determined based on a relationship between a natural frequency and a natural mode because the order of the vibration property in which the value of a natural frequency is reduced becomes apparent by comparing a natural frequency under sound conditions with a natural frequency at the time of evaluation for every order of the vibration property.